The present invention relates to vehicle status measurement systems, and more particularly, to automotive performance meters for use within vehicles.
Performance car drivers are constantly looking for ways to improve their vehicle's performance and their own driving performance, including maximizing their vehicle's, acceleration.
In one common approach to improving acceleration, a driver tries to change or shift gears while the vehicle's engine is operating within what the driver perceives is an optimal revolutions-per-minute (RPM) range. If the shift is performed within that optimal range, the driver will maximize the average power delivered to the wheels by the engine. In contrast, when gear shifting is performed beyond the optimal range, the rate of acceleration decreases even though the vehicle's RPMs continue to increase. When gear shifting is performed before the optimal RPM range, after shifting, the vehicle will often accelerate sluggishly.
To maximize acceleration from an engine, the engine should be kept in an RPM range that allows the gearbox to deliver an optimum level of power to the wheels just before and just after each gear change. When shifting up, there is typically a loss of RPM, and a gain in RPM when shifting down.
Such changes in RPM occur because there are finite gear ratios in the typical vehicle gearbox. The engine shaft is disconnected from the gearbox, driveshaft, and wheels by means of a clutch. When starting from a stop (engine shaft turning at idle, but wheels not turning at all) the clutch slips until the car has gained enough speed so that the wheels, driveshaft, and gearbox are matched in RPMs with the engine. As vehicle speed increases, the engine reaches its maximum allowed RPM. If the driver wants to further increase vehicle speed, gears must be shifted so that the engine can return to a lower number of RPM while the gearbox/driveshaft/wheels continue increasing RPMs.
Within an optimal RPM range for a vehicle, there is an optimal “shift point,” that is, a point in an RPM versus horsepower curve at which the driver of a vehicle should shift gears to maximize average vehicle acceleration. Specifically, the optimal shift point of a vehicle corresponds to a predetermined angular velocity of the motor shaft (i.e., RPM value) that results in maximum power being delivered by the engine to the wheels, both before and after shifting. A graph of the power output of an engine (vertical axis) verses RPMs (horizontal axis) increases to a maximum and then falls off.
Beyond a certain point, increasing RPMs no longer translates into increased power, and thereby vehicle speed, even though more RPMs represent more combustions in the engine per unit time. Rather, the increased RPMs create increased losses, such as vibrations, and other power drains known to those skilled in the art. Also above a certain RPM level (e.g., the “redline” RPM value), an engine can be damaged. Thus, to maintain maximum vehicle speeds, it is desirable to maintain high but not too high RPMs levels.
While drivers, and more aptly, amateur and professional racers, attempt to shift within an optimal RPM range, and ideally at a particular shift point, actually identifying the optimal range and shift point for a particular vehicle and gear is very difficult. Some amateur racers, for example, simply arbitrarily select a shift point, such as an RPM level just below their vehicle's “red line” RPM level. On the other hand, professional racecar drivers spend significant resources analyzing their engines and gearboxes to determine optimal shift points for their vehicles.
Conventionally, shift points are approximately determined under controlled experimental conditions. Determining them involves measuring and then analyzing a particular vehicle's output power versus RPM curves. To generate these curves, one typically measures vehicle power output with a stationary dynamometer. These measurements are then combined with gearbox gear ratios to determine optimal shift points. Although shift points are determined from these curves, the curves, and therefore, the shift points, generally do not account for numerous variables, such as aerodynamic drag, vehicle rolling friction, and drivetrain losses, and other factors which come into play as the vehicle is being driven. Furthermore, such shift points generally must be recalculated when modifications that change the vehicle's RPM and output power characteristics are made to the vehicle.
Accordingly, there is a need for methods and systems that indicate to racers, performance drivers, motor sport enthusiasts and others, optimal RPM ranges and shift points for their vehicles that are low cost, easy to install, and do not require the user to perform complicated and time-consuming analyses of their engines.
Furthermore, there is a need for methods and systems that provide optimal RPM ranges and shift points in a manner that is transparent to the driver, and that dynamically account for variables associated with a moving vehicle, including aerodynamic drag, rolling friction, and drive train losses.